Signaling within a telecommunications network is a fundamental operation and diverse techniques have been developed over time to facilitate use of its various forms. Generally, the term "signaling" denotes the use of call control signals to establish an end-to-end connection through a telecommunications network and to provide for disconnection once a call is complete. In the field of telephony, call control signals provide for either supervision, addressing, or call progress. For example, supervisory call control signals include those indicative of the busy or idle status of a circuit (e.g., on or off hook), addressing signals include those indicative of the station being called (e.g., the called station's telephone number), and call progress signals include those for the establishment of connections through the network (e.g., the ringing signal).
With the increasing use of digital techniques, and with growing demands for higher speeds (e.g., broader bandwidth) and more diversity in the equipment between which communications might be established (e.g., computers, facsimile machines, local area networks), a corresponding need has developed for improvements in call control signaling. It has become particularly desirable to conduct call control signaling with (and within) a switched telecommunications network so that a user can dial up wideband data transport on demand. Such dial-up capabilities have heretofore generally been unavailable.
While various techniques have evolved to advance the signaling art no single technique has been entirely satisfactory for all applications. Basically there are two types of signaling: in-band and out-of-band. With in-band digital signaling, for example, as has been used in telephone systems, certain of the quantizing data bits are robbed from the user data stream for use in conveying signaling information. This results in a loss of signal integrity or resolution since data bits otherwise available for user information are "robbed" for signaling.
Another, relatively recent technique, and generally an advance over the presently available in-band methods, is that of common channel signaling. With this out-of-band method the signals are exchanged between switching system processors over a dedicated network rather than over the data transmission path. Although there is an improvement in signaling speed, and flexibility is gained without quantization loss, there is a necessity for physically separate, dedicated links (aside from the main circuit path) and for data base processing at each end of a link.
Thus, a need persists for simple, low cost, in-band call control signaling methods and apparatus which are operative at the higher digital speeds, which are compatible with the existing digital multiplex hierarchy, and which remain operatively transparent to call control signals formatted and intended for use with certain prior call control signaling techniques and equipment.
Accordingly, it is among the objects of the present invention to provide a simple, in-band call control signaling method and apparatus which meets the above-described needs, which will be operative with dial-up on demand data transport services, and which, without loss of quantization, avoids reliance on separate signaling lines, circuits, and associated data processors.